DESCRIPT ►.ON
TITLE OF INVENTION: FORMING METHOD OF METAL MEMBER
EXCELLENT IN SHAPE FREEZING PROPERTY
TECHNICAL FIELD
[0001] The present invention relates to a forming
method that improves the shape freezing property of a
metal member such as a hat=shaped cross section
member having a bent portion in its longitudinal
direction that is used for a structure member of an
automobile vehicle body, for examples
BACKGROUND ART
[0002] In recent years, there has been often used a
member whose cross section perpendicular to its
longitudinal direction has a hat shape, (which will
be called a hat--shaped cross section member_
hereinafter,) for a structure member of an automobile
vehicle body. A hat shaped cross section member 1 is
formed and worked into a shape depicted in Fig. 1,
for example, and has a bent portion 2 bent in its
longitudinal direction with flange portions
positioned outsides
[0003] In the case when the hat shaped cross section
member is formed and worked so as to have the
portion 2 as above, springback ascribable to residual
stress occurs, and as indicated by a dotted line in
Fig. 2, hanging down in three dimensional directions
occurs in the longitudinal direction based on the
bending point o The correction of this hang down
shape cannot be conducted by the correction of
springback in a conventional two--dimensional shape
(an opening of a U shaped cross section in a cross
section taken along II in Fig. 1)o Note that an
amount of springback is defined to be the value of an
amount of hang down in the vertical direction from
the desired shape of a tip portion of a product.
[0004] As above, in the forming of the hat°shaped
cross section member, securing the shape freezing
property is a very important technical challenge.
CITATION LIST
PATENT LITERATURE
[0005] Patent Literature 1: Japanese Laid open
Patent Publication No, 2004-18'1502
Patent Literature 2: Japanese Laid open Patent
Publication No. 200721568
SUMMARY OF INVENTION
SOLUTION TO PLOBLEM
[0006] In order to secure the shape freezing
property, in Patent Literature 1, for example, there
has been proposed a working method in which by using
a punch having a projecting portion that projects
toward a metal sheet and has a semicircular='shaped
cross section in its head portion, the projecting
portion of the punch is brought into contact with the
portion of the metal sheet to be a wall portion of a
hat-shaped cross section to perform a preliminary
work in which the portion, of the metal sheet, to be
head portion 1s fox:med into a projecting shape
rojecti_ng outward, and next to perform a finishing
work by using a punch for obtaining a predetermined
hat shape. However, this working method is a working
method for a hat6Yshaped cross section member having a
certain shape in an axial longitudinal direction, and
further is a technique that is applicable only to a
two dimensional warp and is not applicable to the
improvement of the hanging down in the three
dimensional shape in the longitudinal direction of
the hat=shaped cross section member 1 having the bent
portion 2 bent in the longitudinal direction with the
flange portions positioned outside as depicted in Fl
1 and Fig, 2.
[0007] Further, in Patent Literature 2, for example,
as for the forming method of the hat=shaped cross
section member having the bent portion in the
longitudinal direction of the member, there has been
proposed a forming method of a hat shaped cross
section member excellent in three dimensional shape
freezing property, in which by using working tools of
a dice, a punch, and a blank holder, in the first
stage forming, the above described member is formed
so that a radius r (mm) of a punch shoulder becomes
larger than a radius H (mm) of a shoulder of a
product, and in the second stage forming, the above
described member is formed so as to have the same
width as that in the first stage forming and to have
the radius R (mm) of the shoulder of the products
However, this forming method is a forming method for
a hat shaped cross section member bent in the
g,
longitudinal direction with flange portions
positioned inside, and is a technique that is not
applicable to the improvement of the hanging down in
the three dimensional shape in the longitudinal
direction of the hat shaped cross section member 1
having the bent portion 2 bent in the longitudinal
direction with the flange portions positioned outside
as depicted in Fig. 1 and Fig. 2®
[0008] As above, there has been a growing need for
improving the shape freezing property of the haL_.
shaped cross section member 1 having the bent portion
2 bent in the longitudinal direction with the flange
portions positioned outside, but no proposition to
improve this has been made currently"
[0009] The present invention has been made in
consideration of the above described challenge, and
has an object to provide a forming method that
improves the shape freezing property of a metal
member having, on its cross section perpendicular to
its longitudinal direction, vertical wall portions on
both sides and flange portions connected to at least
one of the vertical wall portions on both sides, and
having a bent portion bent in the longitudinal.
direction with the flange portions positioned outside
SOLUTION TO PROBLEM
[0010] A forming method of a metal member excellent
in shape freezing property of the present invention
being a method of forming a metal member having,
its cross section perpendicular to its longtudinal.
direction vertical wall portions on both sides and
flange portions connected to at least one of the
vertical wall portions on both sides , and having a
bent portion bent in the longitudinal direction with
the flange portions positioned outside by using
punches and dices , the forming method includes:
setting a dice shoulder radius of the dice for
obtaining a final shape of the metal member to Roo
forming the metal member one time or a plurality of
times by the dice having a dice shoulder radius It1
larger than the dice shoulder radius R0 , arid then
forming the metal member by the dice having the dice
shoulder radius R0.
Further, another characteristic of the forming
method of the metal member excellent in shape
freezing property of the present invention lies in
the point that the dice shoulder radius Ri is set to
fall within a range of not less than lalR0 nor more
than 3a5R0
Further, another characteristic of the forming
method of the metal member excellent in shape
freezing property of the present invention lies in
the point that the metal member has, on its cross
section perpendicular to its longitudinal direction,
vertical wall portions on both sides, flange portions
connected to at l east one of the vertical wall
portions on both sides , and a top sheet portion
connected to the vertical wall portions, and has a
bent portion bent in the longitudinal direction with
the flange portions positioned outside.
Further, another characteristic of the forming
method of the metal member excellent in shape
freezing property of the present invention lies in
the point that the metal member is a hat=shaped cross
section member,
ADVANTAGEOUS EFFECTS OF INVENTION
[0011] According to the present invention, in a
metal member having, on its cross section
perpendicular to its longitudinal direction, vertical
wall portions on both sides and flange portions
connected to at least one of the vertical wall
portions on both sides, and having a bent portion
bent in the longitudinal direction with the flange
portions positioned outside, it is possible to
drastically decrease hanging down caused by
springback in the longitudinal direction and improve
the shape freezing property.
BRIEF DESCRIPTION OF DRAWINGS
[0012] [Fig. ] Fig. 1 is a view depicting a
product shape of a hat shaped cross section member;
[Fig. 2] Fig. 2 is a view depicting a state of
springbuck after the hat---shaped cross section rnember
is formed;
[Fig. 3] Fig. 3 is a view depicting working tools
for forming the hat-shaped cross section member;
[Fig. 4A] Fig. 4A is a view depicting
dist.ribut_ion of stress causing springback in forming
of the hat.fshaped cross section member on a cross
section taken along ii in Fig, 1 by a conventional
forming method;
[Fig. 4B] Fig. 4B is a view depicting
distribution of stress causing springback in forming
the hat-shaped cross section member on the cross
section taken along II in Fig. 1 by a forming method
of a hat shaped cross section member of an
embodiment;
[Fig. 5] Fig. 5 is a view depicting a forming
state on the cross section taken along I==I in Fig.. 1
in the forming method of the hat shaped cross section
member of this embodiment;
[Fig. 6] Fig. 6 is a flowchart depicting a
procedure of the forming method of the hat=shaped
cross section member of this embodiment;
[Fig. 7] Fig. 7 is a view depicting an effect of
which springback is improved by examples;
[Fig. 8A] Fig. 8A is a view depicting an example
of a metal member to which the present invention is
applicable
[Fig. 8B] Fig. 8B is a view depicting an example
of the metal member to which the present invention is
applicable; and
[Fig. 80] Fig o 80 is a view depicting an example
of the metal member to which the present invention is
applicable.
DFSCRIP :[ ON OF EMBODIMENTS
[0013] Hereinafter, a. preferred embodiment of the
present invention will be explained with reference to
the attached drawings.
A hat--shaped cross section member 1 being a metal
member formed by this embodiment is formed and worked
into a shape depicted in Fig. 1. That is, the hatshaped
cross section member 1 has, on its cross
section perpendicular to its longitudinal, direction
(for example, a cross section Laken along I,-I),
vertical wall portions lb and lb on both sides,
flange portions la and la on both sides connected to
the respective vertical wall portions lb and lb, and
a top sheet portion lc connected to the vertical wall
portions lb and lb on both sides, and has a bent
portion 2 bent in the longitudinal direction with the
flange portions la and la positioned outside, I
other words, with the top sheet portion 1c positioned
inside.
[0014] In the case when the hat--shaped cross section
member 1 as above is formed, as depicted in Fig. 3,
by using working tools including a punch 5, a dice 4,
and a not--depicted blank holder as necessary, a steel
sheet 3 is formed and worked.
[0015] Fig. 4A is a view depicting distribution of
stress causing springback in forming of the hatshaped
cross section member on the cross section
taken along 1-1 in Fig. 1 by a conventional forming
method, namely by press forming one time. In the
conventional forming, as depicted in Fig 4A, large
tensile stress occurs in the flange portions la and
la of the bent portion 2 mainly, and further large
compressive stress occurs in a punch bottom (the top
sheet portion 1c) of the bent portion 2. These
tensile-compressive stresses become driving force,
and thereby large hanging down of a product in the
longitudinal direction that starts from the bent
portion 2 occurs, and thus the shape accuracy of the
product deteriorates.
[0016] Thus, the present inventor conducted a
diligent examination in order to minimize the balance
of the above-described tensile-compressive stresses,
and as depicted in Fig. 5, devised to perform press
forming at two stages. Fig. 5 is a view depicting a
forming state on the cross section taken along I- in
Fig. 1 in a forming method of a hat-shaped cross
section member of this embodiment. Incidentally, in
Fig. 5, the reference numerals 6 denote a dice
shoulder of the dice 4 and a dice shoulder of the
steel sheet 3. Further, Fig. 6 is a flowchart
depicting a procedure of the forming method of the
hat=shaped cross section member of this embodiment.
[0017] A dice shoulder radius of the dice 4 for
obtaining the final shape is set to Ro [mm]. In the
forming at the first stage, the hat _shaped cross
section member is formed by the dice 4 having a dice
shoulder radius Rl [mm] larger than the dice shoulder
radius Ro [mm] (Step SiOl) to make only the tensile
stress act in the flange portions la and 1a of the
bent portion 2. The state a in Fig, 5 depicts the
steel sheet 3 at the time when the first stage has
finished. The dice shoulder radius R1 is preferably
set to fall. within a range of not less than 1,180 nor
more than 3.5R0, The reason why the dice shoulder
radius R1 is set to 3,5Ro or less is because if the
dice shoulder radius R1 is too large, wrinkles tend to
be formed on a formed article easily.
[0018] Next, in the forming at the second stage, as
depicted in the state b and the state c in Fig. 5, by
the dice 4 having the dice shoulder radius Ro [mm],
the hat-shaped cross section member is formed inl_:o
the final shape (Step 5102)
[0019] The punch width at the first stage and the
punch width at the second stage are both set to the
same. Further, in the forming at the first stage,
the dice shoulder radius R1 is desirably applied to
the entire area in the longitudinal direction of the
hat-shaped cross section member including the bent
portion 2, but the dice shoulder radius R1 can also be
applied to part of the hat=shaped cross section
member, for example, only the vicinity of the bent
portion 2.
[0020] Fig. 4B is a view depicting distribution of
stress causing springback in the forming of the hatshaped
cross section member on the cross section
taken along 1---I in Fig. 1 according to the forming
method of the hat--shaped cross section member of this
embodiment. By performing the press forming at two
stages, the ten si_l.e stv ress in, the flange portions la
and la of the bent portion 2 is extremely decreased
10
as compared to the tensile stress in the flange
portions la and la depicted in Fig. 4A, and in the
final. shape, the stress relaxed in a compressing
direction acts in the flange portions la and la, and
thereby the balance of the tensile-compressive
stresses can be minimized. By applying the forming
method as above, the tensile stress to occur in the
flange portions la and la of the bent portion 2 can
be corrected in the compressing direction, and
hanging down caused by springback in the longitudinal
direction can be decreased drastically.
EXAMPLE
[0021) As depicted in Fig, 1, the hat-,shaped cross
section member 1 having a length of 500 [mm], a hat
head portion width (a Lop sheet portion width) of 40
[mm], a width between edges of the flange portions la
and la of 100 [mm], and a vertical wall portion
length of 50 [mm] was formed and worked so as to have
the bent portion 2 having a radius Rb: 300 [mm] (a
bending angle: about 170 [° ]) in the middle portion
in the longitudinal direction.
[0022] In a present invention example, in the
forming at the first stage depicted in the state a in
Fig. 5, the hat shaped cross section member 1 was
formed larger with the dice shoulder radius Rl [mm] of
the bent portion 2 set to 125R0: 10 [mm] being 1.25
times the dice shoulder radius R0: 8 [ram] to make the
tensile stress act in the flange portions la and la
Next, as depicted in the state b in fig. 5, the punch
It
width was set to the same as that at the first stage,
and by using the dice 4 having the dice shoulder
radius Ro; 8 [mm], the hat-shaped cross section member
1 was formed and worked to correct the tensile stress
to occur in the flange portions la and la in the
compressing direction,
[0023] Similarly, in another present invention
example, in the forming at the first stage depicted
in the state a in Fig. 5, the hat-shaped cross
section member 1 was formed larger with the dice
shoulder radius Rl [mm] of the bent portion 2 set to
lo5Roo 12 [mm] being 1>5 times the dice shoulder
radius Roe 8 [mm] to make the tensile stress act in
the flange portions la and la. Next, as depicted in
the state b in Vigo 5, the punch width was set to the
same as that at the first stage, and by using the
dice 4 having the dice shoulder radius R0: 8 [mm], the
hat-shaped cross section member 1 was formed and
worked to correct the tensile stress to occur in the
flange portions la and la in the compressing
direction,
[0024] On the other hand, as a comparative example,
by using the dice 4 having a dice shoulder radius R:
8 [mm], the hat-shaped cross section member was
formed and worked at the single stage as directed by
the conventional method.
[0025] As a result, as depicted in Fig. 7, in -the
comparative example, the amount of springback reached
up to about 4.42 [mm], which was extremely large o In
12
contrast to this, in the present invention example in
which the dice shoulder radius R1 [mm] of the bent
portion 2 was set to 1o5Ro: 12 [mm] in the forming at
the first stage, the amount of springback became
about 2096 [mm], and a surprising effect of which the
amount of springback was improved by up to about 33%
was able to be achieved.
[0026] In Table 1, the relationship between the
ratio of the dice shoulder radii R1/Ro and the amount
of springback is depicted. As depicted in Table 1,
as compared to the case of R1/Ro = 1, namely the case
of the hat-shaped cross section member being formed
and worked at the single stage as indicated by the
conventional method, by increasing R1/Ro, the amount
of springback was able to be decreased. The more
R1/Ro was increased, the less the amount of springback
became, but when the dice shoulder radius R1 being in
excess of 3 0 5Ro as is in the case of R1/R0 = 3. 8, poor
forming occurred.
[0027] [Table 1]
R1/Ro AMOUNT OF SPRINGBACK
NOTE
[mm]
100 -4.42 CONVENTIONAL METHOD
RECOMMENDED VALUE LOWER
"l..1 -3A
LIMIT
1.5 -_Y =2096
2.0
---
-2.8
2 ^ 5 --2074
300 _-2.072
RECOMMENDED VALU E UPPER
3.5 2 0 7"I
LIMIT
3A POOR FORMING OCURRDD
13 -=
[0028] In the foregoing, the present invention has
been explained with various embodiments, but the
present invention is not limited only to these
embodiments and may be changed within the scope of
the present invention. For example, in the above.
described embodiment, the example where the press
forming was performed at the two stages has been
explained, but the press forming may also be
performed at three stages or more, That is, the hatshaped
cross section member 1 is formed a plurality
of times by the dice having the dice shoulder radius
R1 larger than the dice shoulder radius Ro. In this
case, the dice shoulder radius R1 is gradually
decreased within a range where the dice shoulder
radius R1 does not become smaller than the dice
shoulder radius Ro. Thereafter, the hat-shaped cross
section member I is formed by the dice having the
dice shoulder radius Roa
[0029] Further, in the above-described embodiment,
the example where the bent portion 2 was bent in the
vertical.. direction with the flange portions la and la
positioned outside (namely the top sheet portion lc
positioned inside) has been explained, but the
present invention is applicable also to the case when
the bent portion 2 is bent obliquely upward with the
top sheet portion 1c positioned inside. That is, the
present invention is applicable to the case when the
bent:. portion 2 is bent so as to contain the component
in the vertical direction with the top sheet portion
lc positioned inside.
[0030] Further, in the above-described embodiment,
the member whose cross section perpendicular to the
longitudinal direction has the hat shape with a
single step has been explained as an example, but the
present invention is applicable also to metal members
whose cross section perpendicular to the longitudinal
direction each have a hat shape with multiple steps
depicted in Fig, SA and Fig. HD, for example.
Further, the present invention is applicable also to
a metal, member having a shape such that the vertical
wall portions lb and lb on both sides and the top
sheet portion lc are smoothly connected on the cross
section perpendicular to the longitudinal direction
depicted in Fig. 8C, for example.
INDUSTRIAL APPLICABILITY
[0031] The present invention makes it possible to
drastically decrease hanging down caused by
springback in the longitudinal direction in a metal
member having, on its cross section perpendicular to
its longitudinal direction, vertical wall portions
and flange portions connected to the above-described
vertical wall portions, and having a bent portion
bent in the longitudinal direction with the abovedescribed
flange portions positioned outside, such as
a hat-shaped cross section member used for a
structure member of an automobile vehicle body, for
example.
l5

CLAIMS
[Claim 1] A forming method of a metal member
excellent in shape freezing property being a method
of forming a metal member having, on its cross
section perpendicular to its longitudinal direction,
vertical wall portions on both sides and flange
portions connected to at least one of the vertical.
wall portions on both sides, and having a bent
portion bent in the longitudinal direction with the
flange portions positioned outside, by using punches
and dices, the forming method comprisingsetting
a dice shoulder radius of the dice for
obtaining a final shape of the metal member to R0,
forming the metal member one time or a plurality
times by the dice having a dice shoulder radius R1
larger than the dice shoulder radius R0, and then
forming the metal member by the dice having the dice
shoulder radius R0.
[Claim 2] The forming method of the metal member
excellent in shape freezing property according to
claim 1, wherein
the dice shoulder radius R1 is set to fall within
a range of not less than lo1Ro nor more than 3a5Rna
[Claim 3] The forming method of the metal member
excellent in shape freezing property according to
claim 1, wherein
the metal member has, on its cross section
pe_rpendi.cular, to its longitudinal. direction, vertical
wall portions on both sides, flange portions
16
connected to at least one of the vertical wall
portions on both sides, and. a top sheet portion
connected to the vertical wall portions, and has a
bent portion bent in the longitudinal direction with
the flange portions positioned outside.
[Claim 4] The forming method of the metal member
excellent in shape freezing property according to
claim 3, wherein
the metal member is a hat-shaped cross section
member.